The present invention is directed to a process for recovering overspray material resulting from the porcelain enameling process of sanitary ware, and more particularly to a recycling process which reuses the collected material in the ground coat enameling operation of sanitary ware.
The porcelain enameling process of sanitary ware such as water closets, sinks, tubs and the like, generally includes a spray coating operation followed by a firing operation. A typical enameling process includes a ground coat application, a drying cycle, a firing cycle, and a cover coat application followed by another drying and firing cycle. During the ground coat and cover coat applications, only a portion of the finely sprayed powder is deposited on the ware. The portion not reaching the ware is called overspray. Depending on the form of the target object and the type of spray coating system, the overspray share of the total consumption of enamel material amounts to about 25 to about 30%.
The collection of overspray material takes place simultaneously with the enameling process. The overspray material is typically collected in dust collection units and includes both ground coat and cover coat material in random ratios. This resulting overspray material is not functional as usable material in the enameling operation because of the undesired mixture of ground coat and cover coat material. Moreover, it is not practical or advantageous to collect the overspray material separately from the dust collection units after each ground coat spray operation and cover coat spray operation. This would be time consuming and very expensive. Therefore, since the overspray material is not usable in its collected state, it must be disposed of or sent back to the enamel supplier. Both of these options include transport and disposal costs which are very expensive. Unfortunately, the disposal of overspray material places a heavy burden on the environment.
The prior art shows several systems for the collection and recycling of overspray paint in an electrostatic painting environment. A number of these systems provide a conduit for returning unused paint powder to the paint supply hopper. Others treat the collected paint with various materials to alter the characteristics of the collected overspray paint. U.S. Pat. Nos. to Coxon et al. (4,044,175) and Vohringer et al. (4,354,451) both teach systems whereby dry overspray paint is collected in a hopper and recycled back into a dry paint supply hopper. The recycled paint may be recycled to the top coat sprayer if only one color is used, or alternatively may be fed back to the undercoat sprayer if nonhomogeneous paint is collected. The paint remains dry throughout the process and is not modified with any additives.
U.S. Pat. Nos. to Richter (4,607,592), Johnson et al. (4,980,030), and Schlumpf et al. (5,292,547), each teach systems whereby the overspray paint is collected from the painting system through the use of water in the spray chamber. This slurry of excess paint and water is then treated with a variety of chemicals to improve the characteristics of the paint. This process includes the addition of chemicals, mixing of the slurry, and concentration of the solution by removing water from the slurry. All of these systems which add chemicals to control the characteristics of the overspray paint collect the paint with water. Therefore, the chemicals are being added to an aqueous solution. All are organic chemical based systems used in paints. None of the prior art processes teach the addition of dry powder to dry collected overspray dust. None of the prior art processes teach a recycling process involving the enameling of sanitary ware.
It is desirable to reduce costs involved in the handling of overspray material collected from the enameling operation of sanitary ware. It is preferable to obviate disposal of the overspray material altogether. It is desirable to utilize inorganic materials as the basic components of a recycling process. It is important to provide a process for recycling the collected overspray material from the enameling operation that is cost-effective and beneficial to the sanitary ware manufacturer.